Catalytic process is the nuclei of modern chemistry and chemical industrial application. Based on the morphology of the catalyst in the reaction process, catalytic process can be classed as heterogeneous catalytic reaction and homogeneous catalytic reaction. At the present time, most of the chemical industrial processes employ heterogeneous catalytic reaction. However, since homogeneous catalytic reaction has the advantages of higher catalytic activity of catalyst used and milder reaction conditions, it continuously serves as an important branch in fundamental research and industrial applications.
The largest difficulty in the wide application of homogeneous catalytic reaction is that it is difficult to separate and recover the catalyst after the completion of the reaction since the homogeneous catalyst used is completely soluble in the reacting system [Advances in Homogeneous Catalysis, Chemical Industry Publisher, Beijing, 1990]. Most of the homogeneous catalysts comprise transition metal that is quite expensive and therefore the problem of separation and recovery of the catalyst will be the key factor determining the economic suitability of the reaction process.
For the moment, there is not yet systematic method for separating and recovering catalyst from reacting system for different kinds of homogeneous catalytic reactions. Some useful attempts have been made in this direction, such as loading the homogeneous catalyst on solid carrier [Catalysis by Supported Complexes, 1981], in which homogeneous catalyst is loaded on inorganic carriers (such as SiO2, diatomaceous earth, active carbon etc.) or bonded chemically to organic polymeric carriers (such as chlorine bead of polystyrene series) to form solid catalyst insoluble in reacting system. By doing so, the catalyst can conveniently be separated and recovered after the reaction ended. However, in this method, the catalytic activity of the homogeneous catalyst is significantly lowered. At the same time, the metal loaded on the carrier will easily be fallen off, resulting in the loss of metal. Therefore there had been only a few practical applications.